The present invention relates generally to a novelly constructed and configured drive system for driving fasteners into a workpiece, and for attaining wedged engagement between a driver and a fastener such that the fastener will be frictionally retained on the end of the driver. More specifically, the invention as illustrated relates to a novel drive bit and drive socket for use with a TORX.RTM. drive system.
Fasteners are a critical component of most structures and mechanisms, from the simplest machine to the highly complex space shuttle. Because of the critical functions performed by these fasteners, improvements in their structure and functional properties are continually sought. One such improvement is the TORX.RTM. drive system, which can be employed, for example, in a drive socket or on a head portion of a fastener, or on a drive bit or socket used for driving such a fastener into a workpiece.
The construction and benefits of the TORX.RTM. drive system are disclosed in U.S. Pat. No. 3,584,667 to Rieland, assigned to the assignee of the present invention. The disclosure of the '667 patent is incorporated herein by this reference. The TORX.RTM. drive represents a significant improvement in the fastener industry.
One such application of the TORX.RTM. drive system is disclose in the patent to Larson et al., U.S. Pat. No. 4,269,246. This patent is also assigned to the assignee of the present invention, and the disclosure thereof is incorporated herein by reference. Specifically, the drive bit of the '246 patent provides means for providing a wedging effect between the bit and a fastener for holding fasteners on the drive bit when the bit is inserted into a recess or socket on the fastener, thereby facilitating one-handed installation of fasteners into a workpiece. This one-handed installation is highly desirable for use in some applications of fasteners where a large number of fasteners are to be installed or inserted into a workpiece, or a plurality of workpieces, such as on an assembly line. This type of frictioned engagement is also desirable where it is preferred to use non-magnetic drives and fasteners. Additionally, the particular construction of the '246 patent helps to prevent "walking" or "wobble" of a fastener, which can cause damage to a workpiece. This "walking" or "wobble" is particularly acute when a pilot hole is not used or during manual installation of self-tapping or self-drilling screws. The drive bit is also self-aligning, which provides significant benefits when utilizing drill screws.
Even though the fastener and the drive bit or assembly provided by the '246 patent are quite effective, there is always room for further improvements and refinements. Specifically, it is to be noted that the drive bit of the '246 patent has a three degree taper on a major diameter thereof. This means that the drive bit makes contact with the fastener at a top of the fastener socket into which the bit is inserted. More definitely, the contact between the bit and the fastener socket occurs at outer, leading edges of lobes on the bit and a center of flutes in the socket. The bit wedges across a major diameter of the bit. Accordingly, the above-discussed wedging effect theoretically occurs at six contact "points," equal in number to the number of flutes and lobes, between the bit and the socket. Because wedging between the bit and the socket occurs only at outside edges of the lobes of the drive bit, high magnitude mechanical stresses can build up at these limited locations. This stress concentration can cause excessive bit wear, as well as loss of dimensional tolerances.
Furthermore, because of the limited contact between the bit and the fastener, a natural tendency arises causing the bit to cam out of the socket in the fastener. Accordingly, there is a potential that the effective lifetime of the drive bit will suffer a reduction, viz. a reduction in ability to prevent wobble, as well as a reduction in the integrity of an interference fit between the bit and the fastener which can make one-handed manual installation more difficult. Additionally, variations in socket fall away, as measured across the major diameter of the socket, which may be difficult to eliminate, can adversely affect depth of penetration of the drive bit into the socket, thereby adding variability of insuring sufficient bit penetration into the socket for driving of the fastener.
A drive system, constructed according to the teachings of the present invention, provides a multilobular drive system which can be embodied in a drive bit, a drive socket, a fastener head post or a fastener socket, which will improve upon the structural and functional characteristics of the drive assembly provided by the above-referenced '246 patent. Specifically, the drive bit of the present invention is configured to wedge in a fastener socket across lobes, between side walls thereof, of the bit. To do this, back-side edges of the lobes of the bit, opposite to the sides thereof which drivingly contact edges of the flutes of the socket, are tapered such that a thickness of the lobes increases from the socket entering end towards the shank of the bit. In this manner, the bit of the invention contacts the socket along the six driving side walls of the bit lobes and the six engaged side walls of the socket flutes, and also contacts the socket at six points proximate the top thereof defined by the engagement between the tapered back-side walls of the bit lobes and the socket flutes, opposite to the engaged side walls thereof. The invention can be employed on a fastener head post in similar fashion.
The multilobular fastener socket of the invention is configured to wedgingly accept a drive bit within flutes, between opposite side walls thereof, of the socket. Specifically, back-side edges of the lobes of the socket, which also define edges of the socket flutes, opposite to the sides thereof which are drivingly contacted by driving edges of the lobes of the drive bit, are tapered such that a width of the socket flutes slopingly decreases, thus causing the thickness of the socket lobes to correspondingly increase, from the socket mouth to the base of the socket. Thus, the socket is contacted by the bit along six driven side walls of the socket flutes, and also at six points proximate the socket base defined by the engagement between the tapered back-side walls of the socket flutes, opposite to the driving side walls thereof, and sides of the bit lobes opposite to the sides thereof in driving engagement with the socket.
It should be noted that engagement at all six lobes, or however many are employed in the multilobular design, is the theoretical maximum. Due to tolerances and wear during use, engagement may occur only at two of three of the drive lobes. Also, while the present invention is illustrated and described with regard to the hexlobular TORX.RTM. drive system, it is applicable to other types of multilobular drive systems.